TPOs are used in many applications, as they are strong, easy to form into final-use parts, and are inexpensive. Unfortunately, TPOs suffer from several deficiencies such as being a soft material, having a narrow thermoforming window, having poor abrasion resistance and having poor weatherability. Impact acrylic polymers are well known for their clarity, toughness, sparkling color, surface gloss, mar resistance and weather resistance.
A composite of an acrylic composition over a TPO would allow the composite to have the best of both materials. Unfortunately, polar acrylic materials do not bond well to non-polar TPOs. Attempts to form composites of these two materials have been plagued by poor adhesion of the layers, especially after temperature cycling.
US 20050069710 describes a multi-layer film of a polyolefin with a functionalized acrylic (polymethylmethacrylate plus a functional acid, acid chloride, alcohol, or anhydride functionality). The multi-layer functionalized film uses a tie layer of an ethylene/alkyl (meth)acrylate/epoxide terpolymer as a tie-layer.
U.S. Pat. No. 6,696,117 describes the use of an ethylene/methyl acrylate/glycidyl methacrylate tie layer to improve the bonding between a fluoropolymer layer and a TPO.
U.S. Pat. No. 6,455,171 describes a composite of an acrylic layer on a polyolefin using a ethylene/methyl acrylate/glycidyl methacrylate tie layer. There is no mention of an impact modified acrylic.
U.S. Pat. No. 6,652,985 claims an acrylic film having an outer layer with a 6-member ring acid anhydride unit, and a tie layer for use over polyolefin based plastic. The outer layer is claimed to contain no acrylic impact modifier.
Surprisingly it has been found that the use of an impact modified acrylic layer, in combination with a functionalized olefin-acrylate-tie layer provides enhanced adhesion of the acrylic layer to the tie-layer and to TPO compared to a (meth)acrylate layer without impact modifier. Additionally, the impact acrylic provides additional impact resistance to the composite and is less detrimental to TPO/acrylic rework blends. Further, the functionalized olefin-acrylate tie layer may be a blend with an impact acrylic, which is easily melt processable on an extruder while the functionalized olefin-acrylate is not as easily processed. The use of the acrylic top layer provides a clear coat/TPO structure that has an improved thermoforming processing window, better abrasion resistance, and improved gloss. The chemical resistance of the top layer is also improved.